Blowout preventers used in hydrocarbon recovery operations have traditionally been manufactured with radially opposing rams that move inward to seal against the tubular, then move outward to let a tool joint pass by the BOP. Each sealing ram contains a relatively large elastomer for accomplishing the desired seal with both the tubular and with the opposing ram.
In order to provide more reliable BOPs capable of withstanding higher pressure differentials, metal inserts have been provided within the elastomer of the BOP rams. U.S. Pat. No. 4,229,012 discloses a ram-type blowout preventer with metal inserts as shown in FIG. 3A. Metal plates are positioned above and below the sealing portions, and a pin extends through each side sealing portion and into the plates. A connecting mechanism is provided for connecting the side portions to a packer ram. The blowout preventer disclosed in U.S. Pat. No. 4,332,367 includes adjoining metal inserts each configured as shown in FIG. 3. The metal inserts disclosed in U.S. Pat. No. 4,444,404 are configured to slide circumferentially with respect to adjoining inserts during the process of expanding or reducing the sealing diameter of the blowout preventer. U.S. Pat. No. 4,550,895 discloses metal reinforcements bars which are embedded in the elastomer of each ram of a BOP. The metal inserts disclosed in U.S. Pat. No. 5,011,110 include circumferentially extending flanges for fitting within the recess of an adjoining insert.
Blowout preventers have used metal inserts which move relative to one another in the manner of an iris to vary the diameter of the BOP bore. U.S. Pat. No. 6,296,225 discloses a BOP with metal inserts designed to move in this manner within each opposing ram of the BOP. U.S. Pat. No. 6,367,804 discloses inserts with a pillar to interconnect the upper body and the lower body of each insert. FIGS. 9 and 11 provide perspective views and a suitable insert according to the '804 patent.
Prior art BOPs have various disadvantages which have limited their acceptance in the oil and gas exploration and recovery industry. Some of the limitations in prior art BOPs concern the large diameter of the blowout preventer, which ideally is as small as possible both in vertical height and in the overall diameter, while also reliably sealing against a wide range of tubular diameters. Although BOPs that use metal inserts are able to withstand higher pressures than BOPs without such inserts, the metal inserts have difficulty with reliably sealing against a high pressure differential across the closed BOP. Improved techniques are thus required to provide a more reliable BOP which does not have the disadvantages of the prior art, may be manufactured and serviced at a relatively low cost, and which substantially minimizes or prevents extrusion of the BOP sealing material.
The disadvantages of the prior art overcome by the present invention. An improved blowout preventer and a sealing ram for the blowout preventer are hereinafter disclosed, with the sealing assembly including a plurality of metal inserts with improved characteristics compared with prior art inserts.